Following Mack [1]} and knowing that Witten diagrams correspond to correlation functions on the boundary (or pieces of the whole correlator), we expect the following Mellin representation,
\(A(P_i)={{\cal N}\over (2\pi i)^{n(n-3)\over 2}} \int _{\Sigma _n}\mathrm {d}\delta _{ij}M(\delta _{ij})\prod _{i<j}^n\Gamma (\delta _{ij})(P_i\cdot P_j)^{-\delta _{ij}}\,,\) 
